monomaniac

• (Received Pronunciation) IPA^(key): /ˌmɒnəʊˈmeɪnɪæk/
• (US) IPA^(key): /ˌmɑnoʊˈmeɪnɪæk/
• Rhymes: -eɪnɪæk

monomaniac (plural monomaniacs)

1. A person who is obsessed with a single thing, to the exclusion of other concerns.

• 1873 — Horatio Alger, Bound to Rise, Ch. X

  Harry knew now that the old man was crazy, or at least a monomaniac, and, though he seemed harmless enough, it was of course possible that he might be dangerous.

• 1890 — Arthur Conan Doyle, The Firm of Girdlestone, Ch. 44

  He had never yet been able to determine whether the old man was a consummate hypocrite or a religious monomaniac.

• (person obsessed): fanatic

monomaniac

1. Focused on one thing above all others.
   • 1851 — Herman Melville, Moby Dick, Ch. 133

     ...then it was that monomaniac Ahab, furious with this tantalizing vicinity of his foe, which placed him all alive and helpless in the very jaws he hated; frenzied with all this, he seized the long bone with his naked hands, and wildly strove to wrench it from its gripe.

• monomania
• monomaniacal